Pyrrole carbonitrile compounds useful as insecticides, acaricides and molluscicides are described in copending patent application Ser. No. 430,601 filed on Nov. 6, 1989. These compounds may be prepared by halogenating pyrrole-3-carbonitrile.
Pyrrole-3-carbonitrile is difficult to synthesize. Literature methods such as that reported by A. M. van Leusen et al., Tetrahedron Letters, 5337, (1972) report yields of 10% or less.
M. S. Morales-Rios et al., Tetrahedron, 45, pages 6439-6448 (1989) disclose the preparation of methyl 2-chloropyrrole-3-carboxylate from methyl 2-cyano-4,4-dimethoxybutyrate and hydrochloric acid. However, methyl 2-chloropyrrole-3-carboxylate is distinct from the 2-halopyrrole-3-carbonitrile compounds prepared by the process of the present invention.
It is therefore an object of the present invention to provide a new and efficient process for preparing 2-halopyrrole-3-carbonitrile compounds.